CWeak evidence, or evidence againstVitamin
The short answer
Sold everywhere for hair and nails on almost no evidence in people who are not deficient, and it can corrupt your blood results. The clearest do-not-bother on this list.
Who this is actually for
Genuine biotin deficiency is very rare outside specific metabolic disorders.
What it is legally allowed to claim
Quoted from the EU register of authorised health claims, Regulation (EU) 432/2012. A product may only make these claims if it supplies enough of the nutrient to qualify.
- Biotin contributes to normal energy-yielding metabolism
- Biotin contributes to the maintenance of normal skin
How much is too much
No EFSA upper level established.
Cautions and interactions
This one matters clinically: high-dose biotin interferes with many laboratory immunoassays, including troponin, thyroid function and some hormone tests. It has caused missed heart attacks and false thyroid diagnoses. Tell any doctor or lab that you take it, and stop it several days before blood tests.
Ask a pharmacist before you start anything. Interactions with prescribed medicines are the most common way supplements cause harm, and they are easy to check. Bring the actual packet, or a photo of the ingredients panel, because doses and forms vary enormously between products. Nothing here is a substitute for advice about your own situation.